Apparatus for exercising the rotary neck muscles of the human body exist in the prior art as evidenced by U.S. Pat. No. 4,278,249 to Forrest and U.S. Pat. No. 4,655,450 to Rogers et al. Such apparatus include head pads which engage the opposite sides of the head while being movable about a vertical axis in response to exertions of the rotary neck muscles to twist or rotate the head from side-to-side. However, such apparatus have no provision for isolating the rotary neck muscles from the torso of the subject which is thus free to assist the rotary neck muscles in performing an exercise thereby lessening efficiency or the effect of the exercise on the rotary neck muscles per se. Moreover, any measurements taken of the strength of the rotary neck muscles may be inaccurate or misleading due to the inclusion of forces generated by the torso.